<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <button class="btn">tap</button>
    <script>
      let city = 'beijing'
      document.querySelector('button').addEventListener('click', () => {
        console.log(city)
      })
    </script>
  </body>
</html>
